Initializes an instance of Watir::Browser using a specified Firefox profile.

initialize_watir_firefox_with_profile.rb

require 'watir'
require 'webdrivers/geckodriver'

# Source:
#  <https://github.com/SeleniumHQ/selenium/issues/7796#issuecomment-555833317>

# Find your Firefox profile's directory by opening 'about:support' in the 
# browser and scrolling down to the 'Profile Directory' field.
# 
# Alternately, to create a new profile, go to 'about:profiles' and click 
# "Create a new profile". When it is created, copy the "Root Directory" path.

@firefox_profile_dir = 'PROFILE PATH GOES HERE'

def init_browser
  profile = @firefox_profile_dir
  service = Selenium::WebDriver::Service.firefox(args: {marionette_port: 2828})
  options = Selenium::WebDriver::Firefox::Options.new(args: ["-profile", profile])
  driver = Selenium::WebDriver.for(:firefox, service: service, options: options)
  @browser = Watir::Browser.new(driver)
end